This invention relates generally to machines and procedures for incremental printing or copying of text or graphics on printing media such as paper, transparency stock, or other glossy media; and more particularly to a machine and method that constructxe2x80x94under direct computer controlxe2x80x94text or images from individual colorant spots created on a printing medium, in a two-dimensional pixel array. For purposes of this document, by the phrases xe2x80x9cincremental printingxe2x80x9d and xe2x80x9cincremental printerxe2x80x9d I mean to encompass all printers and copiers that perform computer-controlled construction of images by small increments.
Incremental printers thereby form images either directly on the print mediumxe2x80x94as in the case of inkjet, dot-matrix or wax-transfer systemsxe2x80x94or on an electro-statically charged drum just before transfer to the medium as in the case of laser printers. Thus by xe2x80x9cincremental printerxe2x80x9d I mean to exclude printing presses, which form a whole image from a previously prepared master negative or plate. The invention employs calibration techniques to optimize color quality and to prevent overinking.
The invention deals with two well-known problems of computer-controlled incremental printers: color quality, and overinking. Color quality will be discussed first.
Reproduction of colors in inkjet printers is greatly affected by factors such as the volume of ink delivered, the type of printing medium, the environmental conditions, and the spatial and temporal rules used to place the colorant on the medium.
In combination, these factors result in a final color rendition that may be very different from what is specified by the computer application. This undesirable result can be further classified into two types of reproduction: lack of accuracy and poor consistency.
By xe2x80x9caccuracyxe2x80x9d I mean the ability of the printer to print the exact color that is requested by the application. By xe2x80x9cconsistencyxe2x80x9d I mean the ability of a population of printers to print always the same color for a given color specification received from the application.
While there are well-known methods to improve color accuracy (usually by providing a color dictionary or color map), color consistency is far more difficult. This is due to the occurrence of factors that vary in a wide range and cannot be predicted at the time of building such color maps.
(a) Inconsistent colorxe2x80x94Two types of solutions have been used heretofore to reduce color-reproduction error due to poor consistency. The more-widely used method creates a so-called xe2x80x9ccalibration profilexe2x80x9d (similar to the color maps mentioned above) that remains valid as long as all the above-mentioned environmental and operational factors remain constant.
Preparing such a calibration profile or color map is time consuming, because many color patches must be printed and measured. It is also relatively costly, because it uses a significant quantity of the final ink and printing mediaxe2x80x94which are expensive in some cases.
It is well worth the effort and cost to prepare such a profile or map once, at the factory, for an entire printer product line, and to ship such a generic profile with each printer produced. This approach, however, has important limitations.
First, such a map preestablished at the factory, if generic to a product line, is inaccurate at the outset for many or most of the printers in the line. Second and more important, even if prepared for each individual printer, a map becomes obsolete whenever any of the printheads is replaced and whenever environmental or operational conditions change.
Third, setting up a printer to automatically make a complete color map for itself in the fieldxe2x80x94that is, after shipment to final users and perhaps even after each change of printhead, or of environmental parametersxe2x80x94is generally unacceptable because of the great time consumption and cost mentioned above. The present market is so highly competitive and demanding as to make the delay and cost alone appear prohibitive.
A known alternative to the use of complete maps or profiles consists of automatically printingxe2x80x94in the fieldxe2x80x94a much smaller number of color patches with each of the printheads, and automatically measuring them with an optical sensor in the printer. Results of these measurements are then incorporated into so-called xe2x80x9ctransfer functionsxe2x80x9d, one for each printhead, which reconcile the expected and measured values.
The transfer functions are then applied, immediately before printing, to color data provided by the application. This second method is far faster and less costly than building complete color maps, but still takes several minutes and still wastes printing medium and ink.
Furthermore, as with the first method, the calculated correction rapidly becomes obsolete with changes in environmental or operating conditions. As a consequence, the process must be repeated very often if the desired consistency in color reproduction is to be maintained. Even with these burdens, the transfer-function approach is less complete than the use of calibration profiles, and therefore inferior in terms of final image quality.
Some prior systems are believed to have included an automatically followed protocol for deciding when to calibrate, for instance when an operator commands it or when an inkjet pen or laser toner cartridge is changed, or when the printing medium is changed. Even with such automatic proceduresxe2x80x94and an optical sensor built into the printer so that the user does not have to actively participate in performance of the map-makingxe2x80x94delay and cost in the present competitive market greatly handicap the transfer-function approach too.
Representative of the second (transfer function) approach is U. S. Pat. No. 5,107,332 of Chan. He teaches use of automatically, continuously field-maintained transfer functions to xe2x80x9ccontinuously update an initial full scale look up table which was initially prepared from a full scale color gamut.xe2x80x9d
It is not completely clear what Chan means by xe2x80x9ccontinuouslyxe2x80x9d, since it would not appear practical to implement that description literally while at the same time printing a desired output image. Presumably his invention instead makes its small test patterns automatically between image printouts or perhaps once a day, or every time a certain number of images has been printed.
It is not my intention to criticize the Chan system, since it undoubtedly functions very well and serves an excellent purpose. As can be seen, however, it does leave some room for further improvement.
Of particular interest are two printer-control languages that have previously been created or adapted for Hewlett Packard (HP) inkjet printers, and particularly large printer/plotters. One of these languages was developed by HP and is known as xe2x80x9cHP-GL/2xe2x80x9d; the other, developed by the Adobe company, is called xe2x80x9cPostScript(copyright)xe2x80x9d. These languages heretofore have remained subject to undesirable print-quality inconsistencies, as discussed above, arising from environmental and operational variations.
The PostScript system has historically employed a transfer-function approach. HP-GL/2 has not.
For printing color images, the PostScript system enables a user to define such functions for whatever purpose the user wishes. A typical usage is for linearization of each ink individuallyxe2x80x94or to linearize a display device with respect to a scanner, or as between two different display devices. Any such defined transfer function is applied by PostScript to the desired image dataxe2x80x94after those data have been interpreted using a principal color calibration profile that nominally interfaces a known image-data source with a known printer.
(b) Inconsistent ink-limiting requirementsxe2x80x94The known technique of ink limiting is used to avoid depositing excessive amounts of ink in some special situations, particularly when printing in certain chromatic inks on certain media, such as glossy stock. For example, it appears that particular inkjet inks contain relatively large pigment molecules that are not readily absorbed into the relatively smaller pores of some glossy media.
To achieve vivid colors in inkjet printing with aqueous inks, and to substantially fill the white space between addressable pixel locations, ample quantities of ink must be deposited. Doing so, however, requires subsequent removal of the water basexe2x80x94by evaporationxe2x80x94and also requires, for some printing media, absorption of the pigment into the medium. These drying phenomena can be unduly time consuming.
In addition, if a large amount of ink is put down all at substantially the same time, within each section of an image, related adverse bulk-colorant effects arise: so-called xe2x80x9cbleedxe2x80x9d of one color into another (particularly noticeable at color boundaries that should be sharp), xe2x80x9cblockingxe2x80x9d or offset of colorant in one printed image onto the back of an adjacent sheet with consequent sticking of the two sheets together (or of one sheet to pieces of the apparatus or to slipcovers used to protect the imaged sheet), and xe2x80x9ccocklexe2x80x9d or puckering of the printing medium.
One situation in which the overinking problem becomes particularly important is in the printing of so-called xe2x80x9cprocess blackxe2x80x9d or xe2x80x9ccomposite blackxe2x80x9dxe2x80x94since ink loading is some three times what it would be for single-ink black. This might seem to suggest that composite black always should be replaced with black ink, but doing so sometimes produces other uncontrollable effects such as changes in the apparent glossiness of the medium, or erratic angular dependencies of the color or reflectance.
Furthermore the use of process black has its own advantages. Process black tends to reduce evident granularity, particularly in highlight regions, andxe2x80x94as some would have itxe2x80x94also produces richer and more interesting shades.
What is needed is a dosing technique that has some potential for at least partially avoiding process-black replacement, and so retaining these benefits of process blackxe2x80x94but that can be carefully controlled. It is necessary to find a way to avoid exceeding the ink-absorption capability of the medium. Ink limiting, which controls overinking directly, can accommodate that capability and so function as an alternative to process-black replacement.
I have recognized, however, that the ink-absorption capability of the medium, like the overall color response discussed in the preceding section, shifts with environmental and other operating conditions. Therefore, as with color consistency, ink limiting is especially problematical when those operating conditions change after an ink-limiting paradigm has been established.
Ink limiting can be of critical importance. For some inkjet systems, glossy stock may be completely unusable without ink limiting; yet prior ink-limiting systems have always been subject to undesirable variation due to environmental conditions and to characteristics of replaceable colorant modules (e. g., inkdrop weights).
(c) Environmental inputsxe2x80x94In some known incremental printers, sensors are used to determine environmental conditions that affect operation of the printer as such, or closely related factors such as image drying time. U. S. Pat. No. 5,617,516 of Barton describes one such inkjet system that monitors temperature and humidity xe2x80x9cfor optimizing printer operationxe2x80x9d. Certain laser (color electrophotography) printers employ like sensors to optimize toner developmentxe2x80x94as through adjusting bias voltage on an image-transfer drum.
In these earlier systems, the optimization of operational settings based on the environmental sensors has necessarily had some indirect or incidental effect on (and usually an improvement of) the quality or even balance of color in printed images. In these devices, however, the environmental measurements have never been used for direct, specific control of color or color balance as such.
(d) Conclusionxe2x80x94As shown above, problems of color consistency and ink-limiting consistency have continued to impede achievement of uniformly excellent inkjet printingxe2x80x94at high throughputxe2x80x94on various industrially important printing media. Thus, important aspects of the technology used in the field of the invention remain amenable to useful refinement.
The present invention introduces such refinement. In its preferred embodiments, the present invention has several aspects or facets that can be used independently, although they are preferably employed together to optimize their benefits.
In preferred embodiments of a first of its facets or aspects, the invention is a method of operating an incremental printer with a printing medium. The method of this first aspect of the invention includes the step of automatically sensing, immediately before printing, at least one environmental condition that affects color of a printed image.
For purposes of this document, by the term xe2x80x9cimmediatelyxe2x80x9d I refer to a time scale that is short in relation to expected changes in environmental conditions of interest. By the phrase xe2x80x9csensing . . . at least one environmental conditionxe2x80x9d I particularly mean sensing such a condition or conditions explicitly; in Chan and the other prior systems discussed earlier, the effects or consequences of such conditions are merely embedded, blind, into each field-generated transfer function or other automatic calibration.
The phrase xe2x80x9cbefore printingxe2x80x9d encompasses the strategy of sensing an environmental condition or conditions before printing an entire image. In addition this phrase encompasses sensing such a condition or conditions during the printing of an entire imagexe2x80x94i. e., just before printing of a particular swath, or of a particular pixel row, or even an individual pixel.
It will be understood too that in this document the word xe2x80x9ccolorxe2x80x9d is used in the larger sense to encompass black as well as chromatic colors. Although the present invention is particularly beneficial in avoiding hue shifts due to environmental changes, it is also useful in linearizing and otherwise improving consistency of even images printed in black or other monochrome colorant.
The method of this first facet of the invention also includes the step of automatically using the sensed environmental condition or conditions to modify operation of the printer, to compensate specifically for effects of the at least one environmental condition on color. This step is performed after the sensing step.
The term xe2x80x9cspecificallyxe2x80x9d is used here to make clear that the invention particularly implements a calculated color correction. In other words this modification does not affect color merely in an incidental way, as for instance in the previously mentioned case of environmentally derived automatic adjustments of prior-art laser printers.
The foregoing may constitute a description or definition of the first facet of the invention in its broadest or most general form. Even in this general form, however, it can be seen that this aspect of the invention significantly mitigates the difficulties left unresolved in the art.
In particular, because this method adjusts itself instantly for one or more external operating conditions, it very straightforwardly avoids color inconsistencies arising from variations in those conditions. As an additional advantage, in purest principle some embodiments of my invention can be made to correct for conditions that change significantly even during printout of a single image.
Although this aspect of the invention in its broad form thus represents a significant advance in the art, it is preferably practiced in conjunction with certain other features or characteristics that further enhance enjoyment of overall benefits. For example, it is preferred that the using step also be in accordance with a color calibration profile that is not prepared immediately before printing.
In other words, what is done in response to variable conditions can be only an adjustment to the overall color calibration for the printer, not a complete calibration with photometric analysis of freshly printed test patterns and so on. Because of this approach, making the correction for environmental conditions takes virtually no time (typically much less than a second) and wastes neither printing medium nor ink. These considerations represent substantial savings by the end user, and also improved productivity.
Another preference is applicable when the method is used with any replaceable colorant-placing module (such as for example an inkjet pen, or a laser-printer toner cartridge) which is selected from multiple such replaceable modules. This preference is applicable if each such particular replaceable module has at least one characteristic distinctive property which affects the color of printed images.
In these cases, preferably the method further includes the step of automatically using information about the distinctive property of the replaceable module to modify operation of the printerxe2x80x94to compensate for effects of the distinctive property on color. In this way the invention avoids color inconsistency arising from variability of not only external conditions but also internal operating conditions.
Other preferences, as mentioned earlier, include combination of this first aspect of the invention with other aspects discussed below. Additionally, some preferences that will be mentioned for the later aspects are applicable to this first facet as well.
In preferred embodiments of a second of its main aspects, the invention is a method of operating an incremental printer, with a printing medium that has a sensitivity to excessive deposition of colorant or a carrier thereof. This method includes the step of automatically sensing, immediately before printing, at least one environmental condition that affects the sensitivity of the medium to excessive deposition of the colorant or carrier.
The method also includes the step of then automatically using the sensed at least one environmental condition to modify operation of the printer, to limit the amount of colorant deposited. This using step thereby avoids excessive colorant or carrier deposition.
The foregoing may constitute a description or definition of the second facet of the invention in its broadest or most general form. Even in this general form, however, it can be seen that this aspect of the invention too significantly mitigates the difficulties left unresolved in the art.
In particular, in this facet of the invention the above-summarized benefits as to color consistency are extended to automatic ink limiting (AIL) insteadxe2x80x94or as well, if the two aspects of the invention are practiced in conjunction.
In preferred embodiments of a third basic aspect or facet, the invention is a method of operating an incremental printer, with a printing medium. The method includes the step of automatically sensing, immediately before printing, at least one environmental condition that affects color of a printed image.
Another step is then automatically applying a combination of a principal color calibration with a transfer function, to modify operation of the printer. A further step is automatically using the sensed at least one environmental condition to modify substantially only the transfer function. In this way the principal calibration is enabled to be a substantially constant characterization of the printer.
The foregoing may consitute a description or definition of the third facet of the invention in its broadest or most general form. Even in this general form, however, it can be seen that this aspect of the invention significantly mitigates difficulties left unresolved in the art.
In particular, preferred embodiments of this third facet of the invention are beneficial in advancing the art of incremental printing: this aspect of the invention focuses upon the advantage of adjusting only a small refinement or correction curve for the overall color-calibration profile of a printer. This is far more efficient than attempting to rebuild that overall profile in the field and in real time.
Although this third aspect of the invention in its broad form thus represents a significant advance in the art, it is preferably practiced in conjunction with certain other features or characteristics that further enhance enjoyment of overall benefits. For example, here too it is preferred that the automatic applying step include using a principal calibration that is not prepared immediately before printing.
This preference in effect exploits the above-noted advantage that it is not necessary to rebuild an overall profile in real time. A far better overall calibration can be prepared at the factory, with superior measuring instruments and the advantages of human evaluation and intervention. Other preferences will appear from the following discussion of other aspects of the invention.
In preferred embodiments of a fourth of its aspects, the invention is an incremental printer for use with a printing medium. The printer includes some means for placing colorant on such medium to form an image. For purposes of breadth and generality in describing my invention, I shall refer to these means as simply the xe2x80x9ccolorant-placing meansxe2x80x9d.
The printer also includes at least one sensor for sensing at least one environmental condition that affects color of the formed image. In addition the printer includes an automatic processor for controlling the placing means to form the image. References throughout this document to a processor or a memory device comprised by the printer shall be understood, even where not expressly indicated, to encompass a processor or memory device in a computer that controls the printer; such relocation of processor and memory functions as between printer and computer is a well-known equivalent.
The processor includes some means for automatically operating the sensor or sensors immediately before printing. These means, again for generality and breadth, I shall call the xe2x80x9csensor operating meansxe2x80x9d.
In addition the processor includes some means for using the sensed at least one environmental condition to modify the controlling of the placing means. These means, once again, I shall call the xe2x80x9cusing meansxe2x80x9d. The modification performed by the using means operates to compensate specifically for effects of the at least one environmental condition on color.
The foregoing may describe or define preferred embodiments of the fourth facet of the invention in its broadest or most general form. The reader will note that this aspect of the invention is closely related to the first (method) aspect discussed earlier, and enjoys similar benefits in the art. I shall discuss here at greater length some of the preferences applicable to both these related method and apparatus forms.
One such preference is that the printer further include some nonvolatile means for holding instructions for automatic operation of the sensor or sensors and the processor, including the environmental-condition using means. Such nonvolatile means may include the memory devices of an interconnected computer, holding a printer driver or other like softwarexe2x80x94or may include a read-only memory (ROM) that holds firmware for controlling the printer processor directly. Alternatively the automatic processor may take the form of an application-specific integrated circuit (ASIC), whose xe2x80x9cinstructionsxe2x80x9d are embedded into the structure of the circuit itself.
Another preference, mentioned earlier as to method aspects of the invention, is that the processor further include some means for performing the placing-means controlling in accordance with a color calibration profile that is not prepared immediately before printing. In this case it is preferable that the printer or driver (or both) further include some nonvolatile means for holding the color calibration profile. Such a profile advantageously is loaded into these nonvolatile means as part of the manufacture of the printerxe2x80x94or, equivalently, of the compilation of a printer driver.
Yet another preference is that the colorant-placing means include at least one particular replaceable colorant-placing module selected from multiple such replaceable modulesxe2x80x94each such module having at least one respective characteristic distinctive property which affects the color of the formed image. In this case the system further preferably includes means, connected to the processor, for providing to the processor information about the distinctive property or properties of each selected replaceable module. To complete this preference, the processor further includes some means for using the distinctive-property information to modify the xe2x80x9ccontrollingxe2x80x9d, to compensate for effects of the distinctive property or properties of each selected replaceable module on color.
Still another preference is that the xe2x80x9cat least onexe2x80x9d sensor include sensors for sensing plural environmental conditions. A yet further preference is that the processor also include means for using the sensed environmental condition or conditions and the distinctive-property information together; here the purpose is to compensate for interactive effects of the environmental condition or conditions, and the distinctive property or properties, on color.
This last-mentioned preference can be particularly important as it avoids the print-quality-degrading effects of assuming independence of the several conditions or properties. By taking into account the environmental conditions and in particular the interactions between themxe2x80x94and their interactions with the inkdrop weight or other distinctive characteristic of a replaceable modulexe2x80x94the system becomes extraordinarily robust, especially when a humidity-sensitive printing medium is in use.
Preferably the invention accommodates environmental conditions such as humidity, pressure, and temperature; and operating conditions such as type and/or color of such media, and resolution; and replaceable-module properties such as magnitude of a quantized colorant quantity (e. g. inkdrop weight) and/or age of the modulexe2x80x94and all preferably with accounting for interactions. Also preferably the information-providing means include means associated with each replaceable module for conveying to the processor information about the respective distinctive property.
For example, my invention can make direct use of inkdrop weight data that have been factory-encoded directly into a simple memory device of an inkjet pen. At run time the printer reads these data from the pen, to establish the drop weight for incorporation into the calculations of my invention. The result is color rendition, color quality, hue balance, etc., that are specifically adjusted for the inkdrops of that particular weight ejected by that particular pen.
As to preferred embodiments of a fifth of its aspects, the invention is an incremental printer for use with a printing medium that has a sensitivity to excessive deposition of colorantxe2x80x94or a carrier of the colorant. The printer includes colorant-placing means, and at least one sensor for sensing at least one environmental condition that affects the sensitivity of the medium to excessive deposition of the colorant or carrier.
The printer also includes an automatic processor for controlling the colorant placing means to form the image. The processor further includes some means for using the sensed environmental condition or conditions to modify operation of the processor, specifically to limit the amount of colorant deposited and so avoid excessive colorant or carrier deposition.
From this it may be seen that the fifth facet of the invention is closely related to the previously introduced second (method) aspect of the invention, and will share many benefits and preferences with that second aspect. At the same time this fifth aspect of the invention shares certain basic preferences with the fourth (apparatus) facet of the inventionxe2x80x94as for example, the incorporation of nonvolatile means for holding operating instructions, and the accommodation of environmental and operating conditions listed earlier.
A sixth aspect or facet of the invention is, in its preferred embodiments, an incremental printer for use with a printing medium. It includes colorant-placing means and at least one sensor for sensing, immediately before printing, at least one environmental condition that affects color of the image. In addition the printer includes an automatic processor for controlling the placing means to form the image.
The processor includes some means for applying a combination of a principal color calibration with a transfer function, to modify the controlling of the placing means, and also some means for using the sensed environmental condition or conditions to modify substantially only the transfer function. In this way the principal color calibration is made a substantially constant characterization of the printer.
The foregoing may be a definition or description of the sixth aspect of the invention. As will be understood this facet of the invention is closely related to the third (apparatus) aspect; and the two share various benefits and preferences.
In preferred embodiments of a seventh of its main aspects, the invention is a method for establishing and using a tabulation of coefficients for use in producing consistent response of an incremental printer. This method is applicable to such a printer whose image characteristics are subject to variable environmental or operating conditions, or both.
The method includes the step of establishing a set of parameters that are the variable environmental or operating conditions, or both. Such parameters for example may include humidity and inkjet drop weight.
The method also includes the step of establishing, for each parameter, values that are anticipated in use of the printer. Thus, continuing the above example, the values may include three to six values of humidity and four to six values of drop weight.
A further step is printing test patterns using crosscombinations of the established values. Still extending the same example, such crosscombinations could include a number of humidity/drop-weight pairsxe2x80x94the actual number being somewhere between 3xc3x974=12 pairs and 6xc3x976=36 pairs, inclusive. If other environmental or operating conditions (for instance temperature and/or printing-medium type) are included in the parameter set, the total number of crosscombinations increases multiplicatively.
(Each test pattern, in turn, most typically consists of crosscombinations of colorant levels for the colorants used in the systemxe2x80x94or if a monochrome system is in use each test pattern consists of a one-dimensional ramp. The idea of such test patterns is generally to canvass the available colors in the system, and, for chromatic systems, to do so particularly near the neutral gray axis.)
Yet another step is photometrically measuring the test patterns. This step produces numerous sets of measurement results, one full set of color specifications for each crosscombination of environmental and operating conditions.
Another step is defining at least one output image specification of interest. For example, for each colorant I define four or five output specifications, which as will be seen include two at endpoints of the system dynamic range and two or three intermediate points. The latter I select, in chromatic printers, to be of maximum usefulness in adjusting the output response for combined chromatic colorants near the neutral-gray color axis.
Another step is, for each crosscombination, calculating photometric error with respect to the at least one defined output specification. In other words, I compare each photometric measurement result with a corresponding one of the defined output image specifications of interest, and subtract to determine the difference.
Now with this array of xe2x80x9cphotometric errorsxe2x80x9d (differences) before us, I begin a two-stage interpretive process. In the first stage, for each crosscombination, I first search or analyze the photometric errors to find an input inking specification that substantially produces the at least one defined output specification.
Here I say xe2x80x9csubstantiallyxe2x80x9d for two reasons. In many cases of greatest practical interest, no single input inking specification can physically produce the defined output. Moreover, even when a single input may in principle produce the defined output, it is not necessary to find a single input that is absolutely precise or accurate in this regard.
In the second stage of the two-stage interpretation, I further analyze the input inking specifications found for the crosscombinations. This step is performed in such a way as to find and tabulate coefficients for use in taking the variable conditions into account, to print a desired image.
Yet another step is storing the coefficients for later application to control operation of the printer. At the outset these coefficients typically reside in general-purpose computers at a design or engineering facility.
In due course these coefficientsxe2x80x94or selected or refined values of themxe2x80x94are stored in printer drivers or in printer ROM modules, or are structurally embedded in ASIC devices. These are provided, with or as part of printer products, to users in the field.
The foregoing may represent a description of definition of the seventh aspect or facet of my invention in its broadest or most general form. Even as couched in these broad terms, however, it can be seen that this facet of the invention importantly advances the art of incremental printing.
In particular, this facet of the invention provides an analytical way, or if preferred a very nearly analytical way, to acquire and accumulate all the numerical information necessary to successful practice of the run-time aspects of the inventionxe2x80x94in hundreds of thousands of units of an incremental printing system, for years thereafter. Furthermore if during the life of such a product line it becomes necessary to update the system for newly available types of printing medium, or for different disposable-module characteristics (such as a new range of drop weights), once again that expanded parameter set or parameter-value set is very readily accommodated by again using the same analytical or nearly analytical procedure.
It should be understood that such updating need not require incorporation into a new printer at the time of manufacture. To the contrary, such updating may require only a new printer driver, or a new firmware ROM, or at most a new ASIC. Such levels of replacement, including the necessary measurements and calculations, may be accomplished as aftermarket activity, either by the original manufacturer directly or by other authorized vendors.
Although the seventh major aspect of the invention thus significantly advances the art, nevertheless to optimize enjoyment of its benefits I prefer to practice this aspect of my invention with additional features or characteristics. In particular, I prefer that the first searching or analyzing step include entering the photometric errors, in association with the corresponding input inking specifications, into a regression calculation.
That calculation fits the calculated photometric errors to at least one colorimetric function. More specifically, as a practical matter, each colorimetric function is normally a function of the input inking specifications.
Another preference is that the entering step include expressing the errors in an algebraically signed form. In earlier efforts employing a more-conventional sum-of-squares or so-called xe2x80x9cenergyxe2x80x9d methodology throughout, I discovered that with such methodology the ability to locate minimum error in this environment is relatively insensitive, and in fact subject to ambiguity. By retaining the algebraic sign of the errors in certain parts of the regression, I preserve the ability to see zero crossings and thereby most precisely locate minimum-error points.
Yet another preference is that the at least one colorimetric function include a family of two-dimensional surfaces in a three-dimensional calculation space. That space has three orthogonal variables, namely: error in one perceptual color dimension, and two varying inks. In this case I further prefer that the first searching or analyzing step further include, for each crosscombination, deducing the input inking specification from the family of two-dimensional surfaces. In using this technique, any one of several tactics may be employed, including:
further evaluating the regression calculations to concurrently match zero photometric error for each of three substantially orthogonal perceptual color dimensions respectively;
for plural candidate input inking specifications, concurrently displaying numerical representations of photometric error values, in a region of the above-described three-dimensional calculation space generally established by the family of two-dimensional surfaces, to facilitate manual selection of one of the candidate specifications based upon consideration of the concurrently displayed numerical representations;
displaying graphical representations of a region of the above-described three-dimensional calculation space generally established by the family of two-dimensional surfaces, for visual interpretation thereof, to facilitate manual selection of the input inking specification therewithin based upon said visual interpretation; and
locating a center of gravity of a geometrical figure bounded, substantially in a zero-photometric-error plane in the three-dimensional calculation space, by the family of two-dimensional surfaces.
Another, more general, preference is that the further analyzing step include entering the input inking specifications into another regression calculation that fits the found input inking specifications to the environmental or operating conditions, or both.
Those skilled in the art will understand that the seventh aspect of my invention as described above is complete when the coefficients have been determined. It will also be understood, however, that eventually the determined coefficients are to be applied to control operation of a printer, and in fact a very large number of printers. Accordingly such application, too, is a preferred step of the seventh aspect of my invention, now under discussion.
That applying step, in turn, preferably includes using the coefficients to produce from input image data a modified form of the input image data, corrected for the environmental or operating conditions or both, for use in controlling the printer to print a desired image.
Preferably the image characteristics to be optimized, through use of the seventh aspect of my invention, include color; and the test patterns include combinations of plural inks of different ink colors. Preferably, for each of the plural inks, the test patterns include multiple inking levels.
For purposes of the seventh main aspect of my invention preferably the parameters are selected from among these: humidity, temperature, pressure, resolution, the type of a printing medium to be used with the printer, the color of such medium, the age of a disposable module (such as an inkjet pen) to be used with the printer, and the magnitude of a quantized colorant quantity (such as inkdrop weight) to be applied by the printer to such medium.
All of the foregoing operational principles and advantages of the present invention will be more fully appreciated upon consideration of the following detailed description, with reference to the appended drawings, of which: